Demography of the Pacific walrus (Odobenus rosmarus divergens) in a changing Arctic

The Pacific walrus (Odobenus rosmarus divergens) is a candidate to be listed as an endangered species under United States law, in part, because of climate change‐related concerns. While the population was known to be declining in the 1980s and 1990s, its recent status has not been determined. We developed Bayesian models of walrus population dynamics to assess the population by synthesizing information on population sizes, age structures, reproductive rates, and harvests for 1974–2015. Candidate models allowed for temporal variation in some or all vital rates, as well as density dependence or density independence in reproduction and calf survival. All selected models indicated that the population underwent a multidecade decline, which began moderating in the 1990s, and that annual reproductive rate and natural calf survival rates rose over time in a density‐dependent manner. However, selected models were equivocal regarding whether the natural juvenile survival rate was constant or decreasing over time. Depending on whether juvenile survival decreased after 1998, the population growth rate either increased during 1999–2015 or stabilized at a lesser level of decline than seen in the 1980s. The probability that the population was still declining in 2015 ranged from 45% to 87%.     

Population structure and speciation in the genus Tursiops based on microsatellite and mitochondrial DNA analyses

Bottlenose dolphins (Tursiops truncatus) have a world-wide distribution, and show morphotypic variation among regions. Distinctions between coastal and pelagic populations have been documented; however, regional patterns of differentiation had not been previously investigated in a wider geographic context. We analysed up to nine different populations from seven different areas of the world by mitochondrial DNA and microsatellite DNA markers, and found differentiation among all putative regional populations. Both mtDNA and microsatellite DNA data show significant differentiation, suggesting restricted gene flow for both males and females. Dolphins in coastal habitat showed less variability and were in most cases differentiated from a pelagic lineage, which could suggest local founder events in some cases. Two coastal populations recently classified as belonging to a new species, T. aduncus, were each highly differentiated from populations of the truncatus morphotype, and from each other, suggesting a possible third species represented by the South African aduncus type.     

Population genetic structure of the lemon shark (Negaprion brevirostris) in the western Atlantic: DNA microsatellite variation

DNA microsatellite markers were used to characterize the population genetic structure of the lemon shark, Negaprion brevirostris, in the western Atlantic. This study demonstrates for the first time the usefulness of microsatellites to study population genetic structure and mating systems in the Chondricthyes. Lemon sharks (mostly juveniles) were sampled non-destructively from four locations, Gullivan Bay and Marquesas Key in Florida, Bimini, Bahamas, and Atol das Rocas, Brazil. At least 545 individuals were genotyped at each of four dinucleotide loci. The number of alleles per locus ranged from 19 to 43, and expected heterozygosities ranged from 0.69 to 0.90. Relatively little genetic structure was found in the western Atlantic, with small but significant values for estimators of F(ST) and R(ST) among populations, theta (0.016) and rho (0.026), respectively. No sharp discontinuities were found between the Caribbean sites and Brazil, and most alleles were found at all four sites, indicating that gene flow occurs throughout the western Atlantic with no evidence for distinct stocks.     

Population genetic structure of the African elephant in Uganda based on variation at mitochondrial and nuclear loci: evidence for male-biased gene flow

A drastic decline has occurred in the size of the Uganda elephant population in the last 40 years, exacerbated by two main factors; an increase in the size of the human population and poaching for ivory. One of the attendant consequences of such a decline is a reduction in the amount of genetic diversity in the surviving populations due to increased effects of random genetic drift. Information about the amount of genetic variation within and between the remaining populations is vital for their future conservation and management. The genetic structure of the African elephant in Uganda was examined using nucleotide variation of mitochondrial control region sequences and four nuclear microsatellite loci in 72 individuals from three localities. Eleven mitochondrial DNA (mtDNA) haplotypes were observed, nine of which were geographically localized. We found significant genetic differentiation between the three populations at the mitochondrial locus while three out of the four microsatellite loci differentiated KV and QE, one locus differentiated KV and MF and no loci differentiated MF and QE. Expected heterozygosity at the four loci varied between 0.51 and 0.84 while nucleotide diversity at the mitochondrial locus was 1.4%. Incongruent patterns of genetic variation within and between populations were revealed by the two genetic systems, and we have explained these in terms of the differences in the effective population sizes of the two genomes and male-biased gene flow between populations.     

Phylogeographic structure and mitochondrial DNA variation in true lemmings (Lemmus) from the Eurasian Arctic

The geographic pattern of mtDNA variation in lemmings from 13 localities throughout the Eurasian Arctic was studied by using eight restriction enzymes and sequencing of the cytochrome b region. These data are used to reveal the vicariant history of Lemmus , and to examine the effect of the last glaciation on mtDNA variation by comparing diversity in formerly glaciated areas to the diversity in non-glaciated areas. Phylogenetic congruence across different Arctic taxa and association between observed discontinuities, and probable Pleistocene barriers, suggest that glacial-interglacial periods were crucial in the vicariant history of Lemmus. Differences in amount of divergence (2.1–9.1%) across different historical barriers indicate chronologically separate vicariant events during the Quaternary. Populations from a formerly glaciated area are no less variable than those in the non-glaciated area. Regardless of glaciation history, no population structure and high haplotype diversity were found within geographic regions. The lack of population structure indicates that populations with high ancestral haplotype diversity shifted their distribution during the Holocene, and that lemmings tracked a changing environment during the Quaternary without reduction of effective population size.     

Nuclear DNA microsatellite analysis of genetic diversity and gene flow in the Scandinavian brown bear (Ursus arctos)

In the 1930s, the Scandinavian brown bear was close to extinction due to vigorous extermination programmes in Norway and Sweden. Increased protection of the brown bear in Scandinavia has resulted in the recovery of four subpopulations, which currently contain close to 1000 individuals. Effective conservation and management of the Scandinavian brown bear requires knowledge of the current levels of genetic diversity and gene flow among the four subpopulations. Earlier studies of mitochondrial DNA (mtDNA) diversity revealed extremely low levels of genetic variation, and population structure that grouped the three northern subpopulations in one genetic clade and the southernmost subpopulation in a second highly divergent clade. In this study, we extended the analysis of genetic diversity and gene flow in the Scandinavian brown bear using data from 19 nuclear DNA microsatellite loci. Results from the nuclear loci were strikingly different than the mtDNA results. Genetic diversity levels in the four subpopulations were equivalent to diversity levels in nonbottlenecked populations from North America, and significantly higher than levels in other bottlenecked and isolated brown bear populations. Gene flow levels between subpopulations ranged from low to moderate and were correlated with geographical distance. The substantial difference in results obtained using mtDNA and nuclear DNA markers stresses the importance of collecting data from both types of genetic markers before interpreting data and making recommendations for the conservation and management of natural populations. Based on the results from the mtDNA and nuclear DNA data sets, we propose one evolutionarily significant unit and four management units for the brown bear in Scandinavia.     

Mitochondrial DNA variation in Atlantic salmon, Salmo, salar L., populations

Mitochondrial DNA (mtDNA) variation was examined in 209 Atlantic salmon from two river systems, the R. Itchen in Hampshire (Southern England) and the R. Conwy (North Wales). Within each system, five spawning sites were sampled. Four enzymes (AVA II, HAE III, HINF I and MBO I) revealed restriction fragment polymorphisms that were informative. Ten clonal lines were observed. These clones were differentially distributed between the two river systems and single clonal types were found to predominate at several spawning sites. MBO I variants were found in salmon from the R. Itchen but not the R. Conwy. A significant heterogeneity in frequency distribution of clonal lines between parr and smolt assemblages of the same year class within the R. Itchen was detected. This heterogeneity suggests that differences in survival or migratory behaviour may be identified by changes in mtDNA clonal frequencies.     

Population genetic structure of North Atlantic, Mediterranean Sea and Sea of Cortez fin whales, Balaenoptera physalus (Linnaeus 1758): analysis of mitochondrial and nuclear loci

Samples were collected from 407 fin whales, Balaenoptera physalus , at four North Atlantic and one Mediterranean Sea summer feeding area as well as the Sea of Cortez in the Pacific Ocean. For each sample, the sex, the sequence of the first 288 nucleotides of the mitochondrial (mt) control region and the genotype at six microsatellite loci were determined. A significant degree of divergence was detected at all nuclear and mt loci between North Atlantic/Mediterranean Sea and the Sea of Cortez. However, the divergence time estimated from the mt sequences was substantially lower than the time elapsed since the rise of the Panama Isthmus, suggesting occasional gene flow between the North Pacific and North Atlantic ocean after the separation of the two oceans. Within the North Atlantic and Mediterranean Sea, significant levels of heterogeneity were observed in the mtDNA between the Mediterranean Sea, the eastern (Spain) and the western (the Gulf of Maine and the Gulf of St Lawrence) North Atlantic. Samples collected off West Greenland and Iceland could not be unequivocally assigned to either of the two areas. The homogeneity tests performed using the nuclear data revealed significant levels of divergence only between the Mediterranean Sea and the Gulf of St Lawrence or West Greenland. In conclusion, our results suggest the existence of several recently diverged populations in the North Atlantic and Mediterranean Sea, possibly with some limited gene flow between adjacent populations, a population structure which is consistent with earlier population models proposed by Kellogg, Ingebrigtsen, and Sergeant.     

Patterns of population subdivision and gene flow in the ant Nothomyrmecia macrops reflected in microsatellite and mitochondrial DNA markers

The Australian endemic ant Nothomyrmecia macrops is renowned for having retained a large proportion of 'primitive' morphological and behavioural characters. Another less studied peculiarity of this species is the production of short-winged (brachypterous) female sexuals, which presumably are poor dispersers. The males, in contrast, bear a full set of normally developed wings and thus may disperse widely. We investigated patterns of genetic differentiation within and among three distantly separated populations in South Australia using nine polymorphic microsatellite loci and four regions of mitochondrial DNA (COI, COII, Cytb, lrRNA). We sampled eight subpopulations, one in the Lake Gilles CP, two near Penong and five around Poochera where distances ranged from 360 km to sites separated by 2-10 km. Only little differentiation was found at the local scale (within the assumed dispersal distance of males) using nuclear markers, whereas the three distant locations were moderately differentiated (FST = 0.06). Mitochondrial DNA genetic structure was much more pronounced on all scales (phiST = 0.98), with regular differences in both haplotype composition and frequency even occurring among closely located sites. This lack of congruence between nuclear and mitochondrial markers strongly suggests limited female dispersal and male-biased gene flow among populations. As to the conservation status of the species there is no evidence for severe population reductions in the recent past, which would have left populations genetically depauperate.     

A review of the genetic relationships of Atlantic walrus (Odobenus rosmarus rosmarus) east and west of Greenland

Studies of the genetic variation involving allozymes, mitochondrial and nuclear DNA (microsatellites) in walruses (Odobenus rosmarus) were reviewed. In addition, the genetic relationships of a total of 211 Atlantic walruses, O. r. rosmarus, from 5 sampling areas west and east of Greenland were studied using 12 nuclear DNA-microsatellite loci and restriction fragment length polymorphism obtained from the ND1, ND2 and ND3/4 segments of the mitochondrial DNA (mtDNA). At the mtDNA level, no divergence was observed among the three sampling areas east of Greenland (i.e. East Greenland, Svalbard and Franz Josef Land), whereas areas west of Greenland (i.e. Northwest and West Greenland) showed some differentiation. The genetic variation at the microsatellite loci grouped the individuals into four sub-populations: Northwest Greenland, West Greenland, East Greenland and a common Svalbard-Franz Josef Land sub-population. A significant correlation between genetic distance and geographic distance between the sampling areas (isolation-by-distance effect) was detected, especially at the mtDNA level. At a small-scale phylo-geographical level, the mtDNA data indicated that Atlantic walruses have diverged into two major groups: one northwest (i.e. in the North Water) and one east of Greenland (i.e. an East Greenland-Svalbard-Franz Josef Land group), whereas the haplotype distribution in the West Greenland sample reflected a mixture of both these groups. The microsatellite data supported a general grouping of walruses to the west and east of Greenland.     

Population structure of the dusky pipefish (Syngnathus floridae) from the Atlantic and Gulf of Mexico,as revealed by mitochondrial DNA and microsatellite analyses

Aim To elucidate the historical phylogeography of the dusky pipefish (Syngnathus floridae) in the North American Atlantic and Gulf of Mexico ocean basins. Location Southern Atlantic Ocean and northern Gulf of Mexico within the continental United States. Methods A 394‐bp fragment of the mitochondrial cytochrome b gene and a 235‐bp fragment of the mitochondrial control region were analysed from individuals from 10 locations. Phylogenetic reconstruction, haplotype network, mismatch distributions and analysis of molecular variance were used to infer population structure between ocean basins and time from population expansion within ocean basins. Six microsatellite loci were also analysed to estimate population structure and gene flow among five populations using genetic distance methods (F_ST, Nei’s genetic distance), isolation by distance (Mantel’s test), coalescent‐based estimates of genetic diversity and migration patterns, Bayesian cluster analysis and bottleneck simulations. Results Mitochondrial analyses revealed significant structuring between ocean basins in both cytochrome b (Φ_ST = 0.361, P < 0.0001; Φ_CT = 0.312, P < 0.02) and control region (Φ_ST = 0.166, P < 0.0001; Φ_CT = 0.128, P < 0.03) sequences. However, phylogenetic reconstructions failed to show reciprocal monophyly in populations between ocean basins. Microsatellite analyses revealed significant population substructuring between all locations sampled except for the two locations that were in closest proximity to each other (global F_ST value = 0.026). Bayesian analysis of microsatellite data also revealed significant population structuring between ocean basins. Coalescent‐based analyses of microsatellite data revealed low migration rates among all sites. Mismatch distribution analysis of mitochondrial loci supports a sudden population expansion in both ocean basins in the late Pleistocene, with the expansion of Atlantic populations occurring more recently. Main conclusions Present‐day populations of S. floridae do not bear the mitochondrial DNA signature of the strong phylogenetic discontinuity between the Atlantic and Gulf coasts of North America commonly observed in other species. Rather, our results suggest that Atlantic and Gulf of Mexico populations of S. floridae are closely related but nevertheless exhibit local and regional population structure. We conclude that the present‐day phylogeographic pattern is the result of a recent population expansion into the Atlantic in the late Pleistocene, and that life‐history traits and ecology may play a pivotal role in shaping the realized geographical distribution pattern of this species.     

Historical sex-specific distribution of Atlantic walrus (<Emphasis Type="Italic">Odobenus rosmarus rosmarus</Emphasis>) in Svalbard assessed by mandible measurements

We developed a discriminant function based on measurements of known-sex mandibles of walrus from the Canadian Arctic collected between 1983 and 1998 and used it to explore the sex ratio in the catches of walrus in Tusenøyane, south-eastern Svalbard, during the nineteenth century. Canadian mandibles older than 5 years of age of known sex were classified into correct sex with 100% accuracy by using two measurements. Applying the same discriminant function to 80 mandibles from Svalbard older than 5 years of age classified 48 (60%) as males and 32 (40%) as females. It also classified 584 aged and un-aged mandibles from Svalbard 67% (390) as males and 33% (194) as females. Eight of the aged jaws (10%) and 41 (7%) of the un-aged jaws had probabilities of classification into sex <80%. We stress the importance of being cautious in applying a discriminant function developed from Canadian mandibles to classify the sex of old weathered mandibles from Svalbard. However, we believe our results indicate that female walrus were once more common in south-eastern Svalbard than they are now.     

Comparing microsatellite variation in north-east Atlantic cod (Gadus morhua L.) to genetic structuring as revealed by the pantophysin (Pan I) locus

Variation at seven microsatellite loci was compared with variation observed at Pan I, a single copy nuclear DNA gene coding for pantophysin, in 14 samples of Atlantic cod ( Gadus morhua ) stretching from Spitsbergen to the North Sea. Population structuring indicated by the two types of markers was concordant and in agreement with the traditional grouping of cod in the study area into three main populations: north-east Arctic cod (NEAC), Norwegian coastal cod (NCC) and North Sea cod (NSC). Microsatellites, however, revealed genetic heterogeneity not only within NCC, as did Pan I, but also within NEAC and NSC, which appeared to be homogenous when analysed for Pan I. Moreover, microsatellites displayed lower levels of differentiation than Pan I between NEAC and two other groups. Differences in the magnitude of differentiation for the two types of markers may be attributable to higher levels of polymorphism and alleged selective neutrality of microsatellites. Isolation by distance was clearly apparent for microsatellites but was less evident for Pan I, indicating that environmentally induced selection appears to shape the patterns of genetic differentiation for this marker. Even though the population structure of north-east Atlantic cod, as revealed by microsatellites and Pan I, appears to be maintained largely by restricted gene flow, selection acting on a recent historical time scale probably contributes to the observed geographic pattern of Pan I frequencies.     

Spatial variation and low diversity in the major histocompatibility complex in walrus (Odobenus rosmarus)

Increased global temperature and associated changes to Arctic habitats will likely result in the northward advance of species, including an influx of pathogens novel to the Arctic. How species respond to these immunological challenges will depend in part on the adaptive potential of their immune response system. We compared levels of genetic diversity at a gene associated with adaptive immune response [Class II major histocompatibility complex (MHC), DQB exon 2] between populations of walrus (Odobenus rosmarus), a sea ice-dependent Arctic species. Walrus was represented by only five MHC DQB alleles, with frequency differences observed between Pacific and Atlantic populations. MHC DQB alleles appear to be under balancing selection, and most (80 %; n = 4/5) of the alleles were observed in walruses from both oceans, suggesting broad scale differences in the frequency of exposure and diversity of pathogens may be influencing levels of heterozygosity at DQB in walruses. Limited genetic diversity at MHC, however, suggests that walrus may have a reduced capacity to respond to novel immunological challenges associated with shifts in ecological communities and environmental stressors predicted for changing climates. This is particularly pertinent for walrus, since reductions in summer sea ice may facilitate both northward expansion of marine species and associated pathogens from more temperate regions, and exchange of marine mammals and associated pathogens through the recently opened Northwest Passage between the Atlantic and Pacific Oceans in the Canadian high Arctic.     

Population structure and impact of supportive breeding inferred from mitochondrial and microsatellite DNA analyses in land-locked Atlantic salmon Salmo salar L.

Four tributaries of Lake St-Jean (Québec, Canada) are used for spawning and juvenile habitat by land-locked Atlantic salmon. Spawning runs have drastically declined since the mid-1980s, and consequently, a supportive-breeding programme was undertaken in 1990. In this study, we analysed seven microsatellite loci and mtDNA, and empirically estimated effective population sizes to test the hypotheses that (i) fish spawning in different tributaries form genetically distinct populations and (ii) the supportive breeding programme causes genetic perturbations on wild populations. Allele frequency distribution, molecular variance and genetic distance estimates all supported the hypothesis of genetic differentiation among salmon from different tributaries. Gene flow among some populations was much more restricted than previously reported for anadromous populations despite the small geographical scale (40 km) involved. Both mtDNA and microsatellites revealed a more pronounced differentiation between populations from two tributaries of a single river compared with their differentiation with a population from a neighbouring river. The comparison of wild and F₁-hatchery fish (produced from breeders originating from the same river) indicated significant changes in allele frequencies and losses of low-frequency alleles but no reduction in heterozygosity. Estimates of variance and inbreeding population size indicated that susceptibility to genetic drift and inbreeding in one population increased by twofold after only one generation of supplementation.     

Population structure and gene flow reversals in Atlantic salmon (Salmo salar) over contemporary and long-term temporal scales: effects of population size and life history

Metapopulation dynamics are increasingly invoked in management and conservation of endangered species. In this context, asymmetrical gene flow patterns can be density dependent, with migration occurring mainly from larger into smaller populations, which may depend on it for their persistence. Using genetic markers, such patterns have recently been documented for various organisms including salmonids, suggesting this may be a more general pattern. However, metapopulation theory does not restrict gene flow asymmetry to 'source-sink' structures, nor need these patterns be constant over longer evolutionary timescales. In anadromous salmonids, gene flow can be expected to be shaped by various selective pressures underlying homing and dispersal ('straying') behaviours. The relative importance of these selective forces will vary spatially and for populations of different census size. Furthermore, the consequences of life-history variation among populations for dispersal and hence gene flow remain poorly quantified. We examine population structure and connectivity in Atlantic salmon (Salmo salar L.) from Newfoundland and Labrador, a region where populations of this species are relatively pristine. Using genetic variation at 13 microsatellite loci from samples (N=1346) collected from a total of 20 rivers, we examine connectivity at several regional and temporal scales and test the hypothesis that the predominant direction of gene flow is from large into small populations. We reject this hypothesis and find that the directionality of migration is affected by the temporal scale over which gene flow is assessed. Whereas large populations tend to function as sources of dispersal over contemporary timescales, such patterns are often changed and even reversed over evolutionary, coalescent-derived timescales. These patterns of population structure furthermore vary between different regions and are compatible with demographic and life-history attributes. We find no evidence for sex-biased dispersal underlying gene flow asymmetry. Our findings caution against generalizations concerning the directionality of gene flow in Atlantic salmon and emphasize the need for detailed regional study, if such information is to be meaningfully applied in conservation and management of salmonids.     

Distribution patterns of the Q and B biotypes of Bemisia tabaci in the Mediterranean Basin based on microsatellite variation

At least five of the biotypes described in the Bemisia tabaci (Gennadius) (Homoptera: Aleyrodidae) complex are known to be present in the Mediterranean Basin area. Only two of them, however, are economically relevant, that is, biotypes B and Q. Biological and genetic differences between the two biotypes have been well studied, but less is known about their patterns of genetic variation and population structure. To address these issues, a study was undertaken based on variation at six microsatellite loci among a subset of nine B. tabaci populations (five belonging to the Q and four to the B biotype). The data obtained show that (i) these loci showed considerable polymorphism in the Q and B biotypes populations although the presence of null alleles can obscure the picture; (ii) the Iberian‐Q, Canarian‐Q, and Egyptian‐B populations exhibit heterozygosity excess as a result of bottleneck events; (iii) the low genetic differentiation between the Israeli, Iberian Peninsula, and Italian populations suggest that these populations share a common gene pool; (iv) the genetic distances between the Canarian‐Q population and the geographically close population from Morocco indicates spatial isolation and a limited gene flow; and finally (v) the microsatellite data for the B populations indicate that the whiteflies from Egypt and Israel have a close phylogenetic relationship, but the source of these biotype B invasions into the Mediterranean area remains unknown.     

Phylogeography, intraspecific structure and sex-biased dispersal of Dall's porpoise, Phocoenoides dalli, revealed by mitochondrial and microsatellite DNA analyses

Mitochondrial DNA (mtDNA) control-region sequences and microsatellite loci length polymorphisms were used to estimate phylogeographical patterns (historical patterns underlying contemporary distribution), intraspecific population structure and gender-biased dispersal of Phocoenoides dalli dalli across its entire range. One-hundred and thirteen animals from several geographical strata were sequenced over 379 bp of mtDNA, resulting in 58 mtDNA haplotypes. Analysis using F(ST) values (based on haplotype frequencies) and phi(ST) values (based on frequencies and genetic distances between haplotypes) yielded statistically significant separation (bootstrap values P < 0.05) among most of the stocks currently used for management purposes. A minimum spanning network of haplotypes showed two very distinctive clusters, differentially occupied by western and eastern populations, with some common widespread haplotypes. This suggests some degree of phyletic radiation from west to east, superimposed on gene flow. Highly male-biased migration was detected for several population comparisons. Nuclear microsatellite DNA markers (119 individuals and six loci) provided additional support for population subdivision and gender-biased dispersal detected in the mtDNA sequences. Analysis using F(ST) values (based on allelic frequencies) yielded statistically significant separation between some, but not all, populations distinguished by mtDNA analysis. R(ST) values (based on frequencies of and genetic distance between alleles) showed no statistically significant subdivision. Again, highly male-biased dispersal was detected for all population comparisons, suggesting, together with morphological and reproductive data, the existence of sexual selection. Our molecular results argue for nine distinct dalli-type populations that should be treated as separate units for management purposes.     

Reduced genetic variation and strong genetic population structure in the freshwater killifish Valencia letourneuxi (Valenciidae) based on nuclear and mitochondrial markers

The genetic variation of the critically endangered Corfu killifish (Valencia letourneuxi), an endemic freshwater fish species of the western Balkans, was assessed for nine populations sampled in eight water systems in western continental Greece, the Peloponnese and the Ionian Island of Corfu, using mitochondrial and microsatellite markers. The analyses were based on data from three mtDNA regions (D‐loop, COI and 16S rRNA sequences) and 14 microsatellite loci. Samples from the congeneric species Valencia hispanica and the phylogenetically closely related species Aphanius fasciatus were also used in the study as outgroups. Both the mitochondrial and the microsatellite analyses revealed three distinct population groupings associated with the geographical distribution of the populations: one southern group occupying rivers draining to the Patraikos Gulf, the second one including the populations flowing into the Amvrakikos Gulf and the third, more northern group, including the other populations from rivers in Corfu Island and Epirus flowing into the Ionian Sea. Within these groupings there is limited genetic differentiation between populations; in addition, there is reduced intrapopulation genetic variation, evidenced by low heterozygosity values, number of alleles and haplotype diversity. In terms of taxonomic implications and appropriate management actions for conservation, our data suggest that the major population groups should be regarded at least as three distinct conservation units (CUs), with translocation and restocking actions to take place only within the geographical range of the CU concerned. © 2013 The Linnean Society of London, Biological Journal of the Linnean Society, 2014, 111 , 334–349.